Rat embryo fibroblasts have been shown to produce MSA (multiplication stimulating activity) an insulin-like growth factor. The MSA produced by the rat embryo fibroblast has been shown to be identical to the MSA species produced by the BRL-3A rat liver cell line on the basis of behavior in polyacrylamide gel electrophoresis and high pressure liquid chromatography. Placental lactogen has been shown to stimulate the biosynthesis of MSA by the rat embryo fibroblasts. An insulin-like growth factor receptor has been purified from chondrocytes isolated from a rat chondrosarcoma. The purified receptor has been shown to have a molecular weight of 220,000 and to display binding characteristics identical to the receptor on intact cells.